1. Field of the Invention
The invention relates to the field of injection molding and, more particularly, to a printed circuit board wiring system for nozzle heaters of an injection molding system.
2. Description of the Related Art
In the field of plastic injection molding, hot runner or "runnerless" injection molding machines are well known and commonly used. In these machines, each cavity of a mold is served, usually by a heated nozzle or "drop" which delivers melted resin from channels in a heated manifold to the respective mold. Recent developments have provided injection molding machines where each nozzle is independently heated and controlled. This independent temperature control is achieved by providing a heater and a temperature sensing device such as a thermocouple at each nozzle, and wiring each heater and thermocouple to a power source/controller which supplies power to the heaters and reads the information supplied by the thermocouples. In a typical 96 cavity mold, however, 192 heater wires and 192 thermocouple wires are necessary to operate the nozzles. Conventionally, these wires are run through channels in the mold manifold plate. This set up, however, requires about 1500 feet of wire, and would typically require about 16 hours to set up. Further, a defective wire is very difficult to locate, and replacement usually involves splicing of the wire. Splices, however, are notorious trouble spots for further problems, and also take up extra space in the already overcrowded wiring channels, which are kept to a minimum size in order to maintain the structural strength of the mold manifold plate. Replacing a defective heater also involves threading a new pair of wires through the existing mass of wiring.
European Patent Application No. 0 468 485, published Jan. 29, 1992, provides a pre-wired hot runner system. In this system, heater wiring is routed in a wiring frame and connected to individual heaters with nuts at each terminal, and forms a series of closed conduits connected to a main junction box. The above-described problems encountered with replacing a faulty wire are not addressed by the European Application.
Further, due to the necessity of minimizing the size of wiring channels in the mold manifold plate, the length of each wire must be carefully optimized in a pre-wired system, resulting in a non-flexible wiring system useful only for a specific number and configuration of cavities.
It is desirable to provide a wiring system for an injection molding machine which overcomes the aforedescribed problems with wiring.
Accordingly, it is the principal object of the present invention to provide a wiring system for an injection molding machine which avoids the use of an excessive mass of wiring.
It is a further object of the present invention to provide such a system which minimizes the size of wiring channels formed in the mold manifold plate.
It is a still further object of the present invention to provide such a system which is serviceable from the front of the machine while installed.
It is another object of the present invention to provide such a system wherein splices are not necessary to correct faulty wiring.
It is still another object of the present invention to provide such a system wherein connection of heaters to the wiring system is achieved through conveniently connected and disconnected plugs.
Other objects and advantages will appear hereinbelow.